The present invention relates to a sheet supply apparatus and a sheet transport apparatus mounted to an image forming apparatus (referred to an image forming apparatus), such as a copier, printer apparatus or a facsimile machine. More particularly, the present invention relates to an automatic supply apparatus detachably mounted to an image forming apparatus and having aligning means for supplying sheets to an image forming apparatus while aligning an edge of the supplied sheets to an alignment reference member.
An image forming apparatus is equipped with a supply portion to supply stacked sheets and image forming means to form images or characters on the sheets supplied from the supply portion. The sheets are transported from the sheet supply portion to the image forming means in a sheet transport path disposed in the image forming apparatus.
In the image forming apparatus, in order to improve the image forming quality by forming the images on predetermined positions on the sheets, the image forming apparatus is equipped with aligning means to supply the sheets to the image forming means while aligning an edge of the sheets supplied from the sheet supply portion to accurately position the sheets. Examples of the image forming apparatus equipped with such aligning means are disclosed in Japanese Patent Publication No. 08-208078 and U.S. Pat. No. 5,494,277.
Apparatuses disclosed in the publications have internal cassette trays for storing the sheets inside the image forming apparatus, and are configured to supply the sheets stacked in the cassette trays to the image forming portion. The number of the sheets stored in the cassette trays is normally approximately from 250 to 500. Thus, when forming an image for a large volume of the sheets at a high speed, it is necessary to frequently replenish sheets. For that reason, an automatic sheet supply apparatus has been required to store a large volume of the sheets.
As shown in Japanese Patent No. 2,625,057 and U.S. Pat. No. 5,368,275, the automatic sheet supply apparatuses with a large capacity are equipped with an elevating paper deck (support stage) for supporting a large volume of stacked sheets (generally from 2,000 to 3,000 sheets), and separating supply means for separating the sheets stacked on the paper deck into a single sheet and for supplying the sheet to a resister roller on the image forming apparatus.
Also, disclosed in Japanese Patent Publication No. 11-30884 as an example, an apparatus installed in the image forming apparatus is configured such that relay rollers arranged at an upstream side in the transport path are separated after the sheet reaches transport rollers at a downstream side to reduce a transport load on the rollers at the downstream side in the transport path when transporting the sheet. One of the rollers is attached to a swinging lever, and a solenoid moves the lever to separate the pair of the relay rollers.
However, there are several problems associated with mounting the conventional large capacity automatic sheet supply apparatus to an image forming apparatus equipped with the aforementioned aligning means.
Firstly, after the sheets from the automatic sheet supply apparatuses reach the alignment means on the image forming apparatus, they are moved in a direction traversing the sheet transport direction along the transport reference. However, when the sheets are nipped in the separating supply means, the sheets are not smoothly moved to the sheet transport reference side. Particularly, in a case that the transport force of the alignment means increases, the sheets might overrun the transport reference, or in the case of thin sheets, their edges might be bent. Further, when the separating supply means remains in a pressing state, it is substantially impossible to do the alignment.
Secondly, it is conceivable to move the sheet transport reference or the alignment means on the sheet automatic sheet supply apparatus to the image forming apparatus side. However, in this case, it is unavoidable to increase a size of the sheet supply apparatus.
Thirdly, the aforementioned sheet supply apparatus needs to have the aligning means since the image forming apparatus performs resister correction for aligning the leading edge of the sheets after separated and supplied, thereby increasing the size of the image forming apparatus. For that reason, if the resister means is eliminated, only the aligning means corrects the sheets, and it is difficult to perform the proper aligning correction for sheets with large bends.